p45^NFE2 Is a Negative Regulator of Erythroid Proliferation Which Contributes to the Progression of Friend Virus-Induced Erythroleukemias

Abstract

In previous studies, we identified a common site of retroviral integration designated Fli-2 in Friend murine leukemia virus (F-MuLV)-induced erythroleukemia cell lines. Insertion of F-MuLV at the Fli-2 locus, which was associated with the loss of the second allele, resulted in the inactivation of the erythroid cell- and megakaryocyte-specific genep45 ^NFE2 . Frequent disruption ofp45 ^NFE2 due to proviral insertion suggests a role for this transcription factor in the progression of Friend virus-induced erythroleukemias. To assess this possibility, erythroleukemia was induced by F-MuLV in p45 ^NFE2 mutant mice. Sincep45 ^NFE2 homozygous mice mostly die at birth, erythroleukemia was induced in +/− and +/+ mice. We demonstrate that +/− mice succumb to the disease moderately but significantly faster than +/+ mice. In addition, the spleens of +/− mice were significantly larger than those of +/+ mice. Of the 37 tumors generated from the +/− and +/+ mice, 10 gave rise to cell lines, all of which were derived from +/− mice. Establishment in culture was associated with the loss of the remaining wild-typep45 ^NFE2 allele in 9 of 10 of these cell lines. The loss of a functional p45^NFE2 in these cell lines was associated with a marked reduction in globin gene expression. Expression of wild-typep45 ^NFE2 in the nonproducer erythroleukemic cells resulted in reduced cell growth and restored the expression of globin genes. Similarly, the expression ofp45 ^NFE2 in these cells also slows tumor growth in vivo. These results indicate thatp45 ^NFE2 functions as an inhibitor of erythroid cell growth and that perturbation of its expression contributes to the progression of Friend erythroleukemia.

ACKNOWLEDGMENTS

We thank Jorge Filmus for his comments on the manuscript and Lynda Woodcock for help in preparation of the manuscript.

This work was supported by a grant from the Medical Research Council of Canada to Y.B.-D. and the National Cancer Institute of Canada to M.A. R.A.S. was supported in part by a grant from the National Institutes of Health. P.A.N. was supported in part by National Institutes of Health grant ROI DK53469, NIH Cancer Center Support grant p30 (CA21762), and the American Lebanese-Syrian Associated Charities. B.J.P and Y.-J.L. were supported by fellowships from the Sunnybrook Trust Fund for Medical Research. R.R.H. was supported by fellowships from the Natural Science and Engineering Research Council (Canada) and the Leukemia Research Fund of Canada.